1. Field of the Invention
The present invention relates to a control method for a vehicle on which a plurality of computers are carried.
2. Description of the Prior Art
In control systems for vehicles such as automobiles, multiprocessor systems each including a plurality of computers have recently been often adopted in order to cope with the increase and complication of control items.
In this case, when any abnormality has occurred, the contents of the RAM of the computer are destroyed, and normal data cannot be held. Therefore, a monitor device for monitoring the occurrence of the abnormality is indispensable. By way of example, the official gazette of Japanese Patent Application Laid-open No. 183254/1988 discloses a monitor device where data are exchanged between two processors insofar as no fault exists, and where the processor causing the error is reset when one of the processors has broken down or when an error has developed in data transfer.
However, in a system wherein the two computers of main and sub ones are connected by communication lines and wherein a control is performed by transferring control data in the ROM of the main computer to the RAM of the sub computer at the time of start, when the occurrence of the abnormality on the sub computer side is dealt with in such a way that the sub computer is reset by an abnormality detection signal from the monitor device so as to clear the contents of the RAM, the resumption of a normal operation becomes difficult. Further, the main computer fails to ensure a normal operation as to a control based on control information from the sub computer.